1. Volume 48, Issue 3, Pages 530-541.e6 (March 2018)
Cbl Ubiquitin Ligases Control B Cell Exit from the Germinal-Center Reaction 
Xin Li, Adeline Gadzinsky, Liying Gong, Haijun Tong, Virginie Calderon, Yue Li, Daisuke Kitamura, Ulf Klein, Wallace Y. Langdon, Fajian Hou, Yong-Rui Zou, Hua Gu 
Immunity 
Volume 48, Issue 3, Pages e6 (March 2018)
DOI: /j.immuni
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2. Immunity 2018 48, 530-541.e6DOI: (10.1016/j.immuni.2018.03.006)
Copyright © 2018 Elsevier Inc. Terms and Conditions

3. Figure 1
Differential Expression of Cbl and Cbl-b in GC DZ and LZ B Cells
(A) qPCR analysis of Cbl and Cbl-b mRNA expression in WT naive and GC B cells. Results were normalized to actin. Expression in naive B cells was arbitrarily defined as 1. Data reflect mean ± SEM of three independent experiments. p < 0.05 (unpaired Student’s t tests).
(B) Immunoblot analysis of Cbl and Cbl-b expression in WT none-GC B and GC B cells. Shown are the results of one representative experiment out of two.
(C) Immunofluorescent staining of Cbl and Cbl-b in the GC DZ and LZ. GC B cells and the LZ were stained by PNA (green) and anti-CD35 (blue), respectively. Cbl and Cbl-b were visualized in red (the scale bar represents 35 μm). Shown are the results of one representative GC out of five individual GCs.
(D) Immunoblot analysis of Cbl and Cbl-b expression in DZ and LZ GC B cells. DZ and LZ GC B cells were purified by FACS as B220+GL7hiFashiCXCR4hiCD86lo and B220+GL7hiFashiCXCR4loCD86hi B cells, respectively. Shown are the results of one representative experiment out of two.
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4. Figure 2 Impaired Antibody Affinity Maturation in Cbl−/− Cbl-b−/− Mice
(A) Kinetics of serum total anti-NP30 antibody titers of IgM and IgG1 isotypes.
(B) The kinetics of serum high-affinity anti-NP4 antibody titers of IgM and IgG1 isotypes.
(C) Antibody affinity maturation of IgG1 antibody. The maturation index is defined by the ratios of anti-NP4 versus anti-NP30 antibody titers.
(D) ELISPOT analysis of splenic ASCs against NP30 or NP4-BSA antigen at day 14 after immunization.
(E) Developmental kinetics of GC B cells in WT and Cbl−/− Cbl-b−/− mice after NP-KLH immunization. Shown are contour maps (left) of GC B cells at day 8 and the statistics (right) of GC B cell numbers after immunization.
(F) Analysis of apoptotic GC B cells. Apoptotic GC B cells were visualized by anti-active-form Casp staining. Shown are contour plots (top panel) and statistical analyses (bottom bars) of Casp+ GC B cells among total B220+GL7hiFashi B cells.
(G) Defective development of high-affinity BCR-expressing GC B cells in Cbl−/− Cbl-b−/− mice. Shown at the left is the gating strategy for splenic B220+NP8-binding B cells and IgG1+CD38− GC B cells among the gated B220+NP8+ cells. Right: statistics of high-affinity (NP8-binding) IgG1 GC B cells in WT and Cbl−/− Cbl-b−/− mice.
Data are means ± SEM (A–G) and are representative of two or three independent experiments with at least four mice per group. ∗p < 0.05; ∗∗p < 0.001; ∗∗∗p < (unpaired Student’s t test).
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5. Figure 3
Impaired Selection of High-Affinity BCRs but Not SHM in Cbl−/− Cbl-b−/− Mice
(A) Pie presentation of the frequency of SHM in VH186.2 genes. VH186.2 genes with different numbers of SHMs are shown in different degrees of shade (right). The total numbers of VH genes analyzed are indicated in the centers of the pies.
(B) Frequency of replacement versus silent mutations in VH186.2 genes. Each dot represents data from one individual VH186.2 gene. Data reflect means ± SEM of individual clones. N.S.: not significant. ∗∗∗ p < (unpaired Student’s t test).
(C) Representation of VH186.2 clones with W33L mutation. The numbers of W33L mutation among total VH186.2 sequences are shown in the center of the pie chart and were compared via Fisher's exact test. ∗∗ p < Data represent 20 VH186.2 clones pooled from five mice in each group.
(D) Ratios of replacement versus silent (R/S) mutations in VH186.2 coding genes.
(E) Development of NIP5 and NP38-binding GC B cells at different time points of the GC reaction. Shown (top panel) are flow-cytometric analyses of splenic NP38 or NIP5-binding cells in gated 220+ GL7hi Fashi GC B cells at days 8 and 14 after NP-KLH immunization. Bottom left and middle: statistics of NP38 and NIP5-binding GC B cells at days 8 and 14 after immunization, respectively. Bottom right: percentages of high-affinity NP (NIP5-binding) GC B cells among total NP-specific (NP38-binding) GC B cells at days 8 and 14 after immunization. Data are means ± SEM (E) and are representative of two independent experiments with five mice per group. ∗∗p < 0.001; ∗∗∗p < (unpaired Student’s t test).
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6. Figure 4
Expedited PC Differentiation of High-Affinity GC B Cells in the Absence of Cbls
(A) In vivo newly generated PCs identified by BrdU labeling assay. Shown are flow-cytometric (left) and statistical (right) analyses of newly generated splenic PCs after 24 hr BrdU labeling; cells were identified as Lin−BrdU+CD138+.
(B) The in vivo rates of PC genesis are presented as the total numbers of newly generated PCs either per spleen (left) or per hour in the spleen (right).
(C) Flow-cytometric analyses of total (top panel) and NIP5-binding (bottom panel) GC B cells at day 12 without (left) or with (right) ER-Cre mediated Cbl ablation. Results of statistical analyses are shown in bars on the right.
(D) In vitro PC differentiation of naive WT and Cbl−/− Cbl-b−/− B cells from Cblfl/fl Cbl-b−/− Mb1-Cre tg mice in 40LB feeder cell culture. Shown are flow-cytometric (left) and statistical (right) analyses of (CD138+ B220hi/lo) PCs/plasma blast-like cells.
(E) Comparison of in vitro differentiation of freshly isolated WT and Cbl−/− Cbl-b−/− (Lin− B220+ GL7hi) GC B cells. Purities of the isolated GC B cells are shown in Figure S9B. Shown are flow-cytometric (left) and statistical (right) analyses of plasma blast-like (B220+ CD138hi) cells generated in the culture.
(F) Cell-division-dependent B cell differentiation to PCs in 40LB feeder culture system. Shown are dot plots (left) and histogram analyses (right) of Irf4 expression in first through fourth cell divisions of WT or Cbl−/− Cbl-b−/− B cells (Cblfl/fl Cbl-b−/− Mb1-Cre tg) identified by cell-trace dilution.
Data are means ± SEM (A–F) and are representative of two or three independent experiments with at least four mice per group. ∗p < 0.05; ∗∗p < (unpaired Student’s t test).
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7. Figure 5
Post-Transcriptional Regulation of GC Differentiation Program by Cbls
(A) qPCR analysis of GC B cell and PC identity genes in WT and Cbl−/− Cbl-b−/− GC B cells. Data were from FACS-purified splenic B220+ GL7hi Fashi GC B cells pooled from 3× WT and Cbl−/− Cbl-b−/− mice at day 8 after SRBC immunization.
(B) Comparison of the expression of protein-synthesis- and secretion-related genes known to be upregulated in PCs in WT and Cbl−/− Cbl-b−/− GC B cells. Shown are the folds of increased expression in Cbl−/− Cbl-b−/− relative to WT GC B cells.
(C) Immunoblot analysis of Irf4 in WT and Cbl−/− Cbl-b−/− B220+ GL7hi CD138− GC B cells GC B cells.
(D and E) Flow-cytometric analyses of Irf4 versus Bcl6 expression in GC B cells without (D) or with (E) anti-CD40 and BCR stimulation. Shown are contour maps (top panel) and results of statistical analyses (bottom panel) of Irf4hi Bcl6lo and Bcl6hi cells among total gated B220+ GL7hi Fashi GC B cells.
(F) Immunoblot analysis of Irf4 expression in WT and Cbl−/− Cbl-b−/− B220+GL7hi CD138- GC B cells with or without anti-CD40 and BCR stimulation.
Data are means ± SEM (A, D, and E) and are representative of two or three independent experiments (A, C, D, E, and F) with at least four mice per group. ∗∗p < 0.001; ∗∗∗p < (unpaired Student’s t test).
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8. Figure 6
Regulation of Nuclear Irf4 Ubiquitination and Expression by Cbls
(A and B) Confocal microscopic analysis of cytosolic and nuclear Irf4 in WT and Cbl−/− Cbl-b−/− GC B cells without (A) or with (B) anti-CD40 and BCR stimulation. The statistical analyses show the percentages of nuclear versus total Irf4. Each dot represents one cell.
(C) Immunoblot analysis of nuclear versus cytosolic Irf4 in WT and Cbl−/− Cbl-b−/− B220+ GL7hi CD138− GC B cells before and after anti-CD40 and BCR stimulation.
(D) Asymmetric expression of Cbl and Cbl-b versus Irf4 proteins in WT B220+ GL7hi CD138− GC B cells before and after CD40 and BCR stimulation.
(E) Co-immunoprecipitation and immunoblot analysis of Cbl and Cbl-b association with Flag-tagged Irf4 (Irf4-Flag).
(F) Irf4 ubiquitination by Cbl or Cbl-b. Shown are immunoblot analyses of ubiquitinated Irf4-Flag immunoprecipitated from 239T cells cotransfected with either Cbl or Cbl-b.
(G) Association of Irf4 with Cbl or Cbl-b in freshly isolated WT GC B cells.
(H) Ubiquitination of Irf4 in WT and Cbl−/− Cbl-b−/− in-vitro-generated GC (iGC) B cells.
Data are means ± SEM (A and B) and are representative of two independent experiments (A–G). ∗∗p < 0.001; ∗∗∗p < (unpaired Student’s t test).
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9. Figure 7 Impaired Development of High-Affinity GC B Cells in Cbl−/−
Cbl-b−/C373A or MSCV-Irf4 BM Chimeric Mice
(A–C) Impaired GC affinity maturation in Cbl−/− Cbl-b−/C373A mice as compared to WT and Cbl−/− Cbl-b−/+ IgCγ-Cre tg controls (day 12 after NP-KLH immunization). (A) Dot plots (top panel) and statistical analyses (bottom bar) of Fas+ GL7+ GC B cells among gated splenic B220+ cells. (B) Flow-cytometric (top panel) and statistical (bottom bar) analyses of high-affinity (NP8-binding) GC B cells among total B220+ cells. Shown are the gating strategy of splenic B220+NP8-binding B cells (top right panel), high-affinity NP specific IgG1+CD38- GC B cells (bottom right panel), and statistical analyses of high-affinity NP-binding GC B cells. (C) Results of statistical analyses of splenic total (anti-NP30-binding antibody) and high-affinity (NP4–binding antibody) secreting plasma cells (ASCs).
(D–F) Ectopic expression of Irf4 abolishes the development of high-affinity-antibody-producing GC B cells in MSCV-Irf4 BM chimeric mice after NP-KLH immunization (day 12). WT BM stem cells were transduced with either MIGR-MSCV-GFP (empty) or MSCV-GFP-Irf4 retroviral vector and used for generating BM chimeras. (D) Dot plots (left) and statistical analyses (right) of Fas versus GL7 staining of the gated B220+ IgD−/lo splenic GC B cells. (E) Contour plots (top) and statistical analyses (bottom) of splenic high-affinity (NP8-binding) IgG1+ CD38− GC B cells in BM chimeras with (GFP+) or without (GFP−) retrovirus infection. (F) Histogram analysis of B220− CD138+ splenic PCs among GFP+ lineage-marker-negative (Lin−) splenocytes in empty MIGR-MSCV and Irf4-MSCV-infected BM chimeras.
Data are means ± SEM (A–F) and are representative of two or three independent experiments with at least five mice per group. ∗p < 0.05; ∗∗p < (unpaired Student’s t test).
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